1. Field of the Invention
The present invention pertains to elongated oil well pump or sucker rods which are fabricated by friction welding elongated cylindrical rod portions to respective large diameter coupling end portions to provide an improved transition zone between the rod portion and the respective end portions.
2. Background
In the art of elongated well pump rods, commonly referred to as sucker rods, many different materials and rod configurations have been developed in an effort to provide long service life and reasonable manufacturing cost and at the same time providing for efficient operation of the well pumping unit. In regard to the last mentioned requirement the ever increasing depth at which liquid hydrocarbons are being produced has brought the increased realization that the sucker rod string comprises a substantial part of the load imposed on the pumping unit. For example, in a well of average depth in the range of 3500 to 4000 feet the use of steel sucker rods represents approximately 60 to 70% of the work load imposed on the pumping unit. Accordingly, there has been a long felt desire to reduce the weight of the sucker rod string while at the same time retaining adequate strength and corrosion resistance to permit suitable service life of the rods. In this regard various materials have been substituted for steel including aluminum alloys and composite rods using fiberglass and other non-metal materials.
The use of wrought aluminum alloys for oil well sucker rods is particularly attractive in that the significantly lower density of the rod material, as compared with steel, and the relatively high tensile strength of certain aluminum alloys provides for a substantial reduction in the weight of the sucker rod string without increasing the working stress on the rods themselves. Moreover, certain aluminum alloys have indicated superior corrosion resistance in most applications of oil well sucker rod pumping units.
However, one problem associated with the use of aluminum sucker rods is in fabrication of the rods to provide the coupling end portions. Upset forging of wrought aluminum alloy rod stock to form the enlarged portions required for the coupling for connecting one rod section to another has been difficult to accomplish with aluminum alloys while retaining the desired mechanical strength characteristics of aluminum. In this regard other means of forming the coupling ends have been sought. Although, friction welding of elongated tubular members has been attempted the provision of suitably welded sucker rods with the required structural integrity has eluded workers in the art prior to the discovery of the present invention.